[Clang][Sema] Add warning when converting bool to character types (with exception of explicitly qualified types, which are aliases to int8_t and uint8_t)

Author: hanickadot

clang/include/clang/AST/Type.h

@@ -2527,6 +2527,8 @@ class alignas(TypeAlignment) Type : public ExtQualsTypeCommonBase {
   bool isAnyCharacterType() const;
   bool isUnicodeCharacterType() const;
   bool isIntegralType(const ASTContext &Ctx) const;
+  bool isExplicitlyQualifiedCharType() const;
+  bool isUnqualifiedCharType() const;
 
   /// Determine whether this type is an integral or enumeration type.
   bool isIntegralOrEnumerationType() const;

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -4348,6 +4348,9 @@ def warn_impcast_constant_value_to_objc_bool : Warning<
   "the only well defined values for 'BOOL' are YES and NO">,
   InGroup<ObjCBoolConstantConversion>;
 
+def warn_impcast_bool_to_character : Warning<
+  "implicit conversion from 'BOOL' to %0">, InGroup<Conversion>;
+
 def warn_impcast_fixed_point_range : Warning<
   "implicit conversion from %0 cannot fit within the range of values for %1">,
   InGroup<ImplicitFixedPointConversion>;

clang/lib/AST/Type.cpp

@@ -2145,6 +2145,20 @@ bool Type::isCharType() const {
   return false;
 }
 
+bool Type::isExplicitlyQualifiedCharType() const {
+  if (const auto *BT = dyn_cast<BuiltinType>(CanonicalType))
+    return BT->getKind() == BuiltinType::UChar ||
+           BT->getKind() == BuiltinType::SChar;
+  return false;
+}
+
+bool Type::isUnqualifiedCharType() const {
+  if (const auto *BT = dyn_cast<BuiltinType>(CanonicalType))
+    return BT->getKind() == BuiltinType::Char_U ||
+           BT->getKind() == BuiltinType::Char_S;
+  return false;
+}
+
 bool Type::isWideCharType() const {
   if (const auto *BT = dyn_cast<BuiltinType>(CanonicalType))
     return BT->getKind() == BuiltinType::WChar_S ||

clang/lib/Sema/SemaChecking.cpp

@@ -11968,6 +11968,23 @@ static const IntegerLiteral *getIntegerLiteral(Expr *E) {
   return IL;
 }
 
+static void DiagnoseFromBoolConversions(Sema &S, QualType T, Expr *E) {
+  E = E->IgnoreParenImpCasts();
+  SourceLocation ExprLoc = E->getExprLoc();
+
+  const Type *Target = S.Context.getCanonicalType(T).getTypePtr();
+  if (Target->isAnyCharacterType() &&
+      !Target->isExplicitlyQualifiedCharType()) {
+    if (S.LangOpts.CPlusPlus) {
+      S.Diag(ExprLoc, diag::warn_impcast_bool_to_character)
+          << T
+          << FixItHint::CreateInsertion(E->getBeginLoc(), "static_cast<bool>(")
+          << FixItHint::CreateInsertion(S.getLocForEndOfToken(E->getEndLoc()),
+                                        ")");
+    }
+  }
+}
+
 static void DiagnoseIntInBoolContext(Sema &S, Expr *E) {
   E = E->IgnoreParenImpCasts();
   SourceLocation ExprLoc = E->getExprLoc();
@@ -12434,6 +12451,9 @@ void Sema::CheckImplicitConversion(Expr *E, QualType T, SourceLocation CC,
   if (Target->isBooleanType())
     DiagnoseIntInBoolContext(*this, E);
 
+  if (Source->isBooleanType())
+    DiagnoseFromBoolConversions(*this, T, E);
+
   if (DiscardingCFIUncheckedCallee(QualType(Source, 0), QualType(Target, 0))) {
     Diag(CC, diag::warn_cast_discards_cfi_unchecked_callee)
         << QualType(Source, 0) << QualType(Target, 0);